The present invention relates to methods of using polishing pads for chemical mechanical planarization (CMP), and in particular, relates to methods of using water-based polishing pads exhibiting improved defectivity.
In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting and dielectric materials are deposited on or removed from a surface of a semiconductor wafer. Thin layers of conducting, semiconducting, and dielectric materials may be deposited by a number of deposition techniques. Common deposition techniques in modern processing include physical vapor deposition (PVD), also known as sputtering, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), and electrochemical plating (ECP).
As layers of materials are sequentially deposited and removed, the uppermost surface of the wafer becomes non-planar. Because subsequent semiconductor processing (e.g., metallization) requires the wafer to have a flat surface, the wafer needs to be planarized. Planarization is useful in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials.
Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize substrates, such as semiconductor wafers. In conventional CMP, a wafer carrier is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the wafer, pressing it against the polishing pad. The pad is moved (e.g., rotated) relative to the wafer by an external driving force. Simultaneously therewith, a chemical composition (“slurry”) or other fluid medium is flowed onto the polishing pad and into the gap between the wafer and the polishing pad. Thus, the wafer surface is polished and made planar by the chemical and mechanical action of the slurry and pad surface.
Casting polymers (e.g., polyurethane) into cakes and cutting (“skiving”) the cakes into several thin polishing pads has proven to be an effective method for manufacturing “hard” polishing pads with consistent reproducible polishing properties. Unfortunately, polyurethane pads produced from the casting and skiving method can have polishing variations arising from a polishing pad's casting location. For example, pads cut from a bottom casting location and a top casting can have different densities and porosities. Furthermore, polishing pads cut from molds of excessive size can have center-to-edge variations in density and porosity within a pad. These variations can adversely affect polishing for the most demanding applications, such as low k patterned wafers.
Also, coagulating polymers utilizing a solvent/non-solvent process to form polishing pads in a web format has proven to be an effective method of manufacturing “soft” polishing pads. This method (i.e., web-format) obviates some of the drawbacks discussed above that is found in the casting and skiving process. Unfortunately, the (organic) solvent that is typically used (e.g., N,N-dimethyl formamide) may be cumbersome and cost prohibitive to handle. In addition, these soft pads may suffer from pad-to-pad variations due to the random placement and structure of the porosities that are formed during the coagulation process.
In addition, polishing pads may be formed by combining two or more pads together. For example, Rutherford et al., in U.S. Pat. No. 6,007,407, discloses polishing pads for performing CMP that are formed by laminating two layers of different materials. The upper polishing layer is attached to a lower layer or “sub-pad” formed from a material suitable for supporting the polishing layer. The sub-pad typically has higher compressibility and lower stiffness than the polishing layer and essentially acts as supporting “cushions” for the polishing layer. Conventionally, the two layers are bonded with a pressure-sensitive adhesive (“PSA”). However, PSAs have relatively low bonding strength and marginal chemical resistance. Consequently, a laminated polishing pad utilizing PSAs tend to cause the sub-pad to separate (“delaminate”) from the upper polishing layer, or vice versa, during polishing, rendering the pad useless and impeding the polishing process.
Thus, there is a demand for a polishing pad with improved density and porosity uniformity. In particular, what is needed is a polishing pad that provides consistent polishing performance, lower defectivity, which resists delamination and is cost effective to manufacture.